The present invention relates to solid-liquid separators, especially used for the treatment of sewage, wastewater, polluted stream water, lake water, storm water or the like.
In conventional granulators/clarifiers having a thickener, solid-liquid separation is carried out by converting pollutants in the influent into densified pellets and thus clarified influent is passed through a clarification zone and discharged as clarified water from an effluent pipe at the top.
However, high influent flow rate causes the following problems resulting in the inclusion of pollutants in treated water.
(1) The upflow rate in the tank not only increases but also varies. Thus, slow-settling pellets are insufficiently separated.
(2) The increased upflow rate in the tank causes insufficient association of some flocs, which are discharged with upflow from the effluent pipe without forming densified pellets.
It is an object of the present invention to solve the above problems of the prior art and to provide a compact solid-liquid separator having a high sedimentation rate by limiting pollutants"" outflow even when flocs are insufficiently pelletized.
In order to solve the above problems, the present invention provides a solid-liquid separator comprising a separation tank, a treated water outlet at the top of the tank, a sludge outlet at the bottom of the tank, a draft tube near the center in an upper inner zone of the tank and connected to a raw water inlet pipe, horizontally rotatable multistage stirring blades A in said draft tube, horizontally rotatable multistage stirring blades B immediately below said draft tube and having a greater diameter than that of said draft tube, a horizontal baffle below said stirring blades B, a filter medium layer consisting of a floating filter medium around the outside of said draft tube above said stirring blades B, and a screen fixed below the water level above said filter medium layer for impeding outflow of said filter medium, whereby the treated water having passed through said screen is discharged from said treated water outlet.
The solid-liquid separator may further comprise a filter medium-receiving screen around the lower outside of said draft tube and stirring rods above the screen or an aeration means. The stirring rods are rotatable and wash the filter medium during washing or even during water feeding. The aeration means aerate the filter medium layer during washing.